The combating of nematodes and soil insects is gaining ever more importance in intensive cultivation of crop plants. Insects which continuously or at times, for example during certain development stages, live in or on the soil or close to the soil, for example on parts of plants, are designated soil insects (compare also B. Homeyer in Chemie der Pflanzenschutz- und Schadlingsbekampfungsmittel [Chemistry of the Plant Protection Agents and Agents for Combating Pests], published by R. Wegler, Volume 1, Springer-Verlag, Berlin 1970, pages 464 to 474). Such pests should preferably be combated preventively so that an agent for combating soil pests must be applied early and must have a reliable and adequate activity for the maximum possible period. It is frequently advantageous for the agents for combating pests already to be applied during sowing, in order to simultaneously achieve protection of the seed and of the developing young plants.
Since the soil treatment agents currently available do not always reliably display an adequately long activity under adverse weather and/or soil conditions, it is an object of the invention to provide new agents for combating pests which allow long-lasting protection of the plants, even under adverse conditions.